In recent years one has become increasingly aware of the impact of human activities on the environment and the negative consequences this may have. Ways to reduce, reuse and recycle resources are becoming more important. In particular, clean water is becoming a scarce commodity. Therefore, various methods and devices for purifying water have been published.
A method for water purification is by capacitive deionization, using an apparatus having a flow through capacitor (FTC) to remove ions in water. The FTC functions as an electrically regenerable cell for capacitive deionization. By charging electrodes, ions are removed from an electrolyte and are held in an electric double layer at the electrodes. The electrodes can be (partially) electrically regenerated to desorb such previously removed ions without adding chemicals.
The apparatus to remove ions comprises one or more pairs of spaced apart electrodes (a cathode and an anode) and a spacer separating the electrodes and allowing water to flow between the electrodes. The electrodes have current collectors or backing layers that are generally adjacent to or very near the electrodes and a material to store the ions. Current collectors are electrically conductive and transport charge in and out of the electrodes.
The apparatus comprises a housing comprising a water inlet to let water in the housing and a water outlet to let water out of the housing. In the housing of the apparatus, the layers of electrodes and spacers are stacked in a “sandwich” fashion by compressive force, normally by mechanical fastening.
A charge barrier may be placed adjacent to an electrode of a flow-through capacitor. The term charge barrier refers to a layer of material which is permeable or semi-permeable and is capable of holding an electric charge. Ions are retained or trapped, on the side of the charge barrier towards which the like-charged ions migrate. A charge barrier may allow an increase in ionic efficiency, which in turn allows energy efficient ion removal.